Hack Pittsburgh did it's "C1" balloon launch on 11/11/12. The balloon carried an Adafruit Ultimate GPS Breakout Board using it's on-module logging feature.
It mostly worked well, but we discovered a minor glitch: at altitudes above 32,767 meters the recorded altitudes wrap around to negative numbers. By comparing the altitudes with the trend before and after the negative numbers, it appears the GPS calculated the altitude correctly, but the wraparound occurred when storing the value in the flash as a 16 bit signed number.
If we correct the negative numbers by adding 65536 we get values that make sense relative to the surrounding numbers.
Using this technique, we logged a max altitude of 34046 meters ( 111,757 feet )
Other Adafruit products were used on the launch and worked well:
Weatherproof 18B20 temperature sensor
Two Adafruit Data Logging Shields
Serail JPEG Camera (watch the Hack Pittsburgh site; we will add the pictures soon)
Hack Pittsburgh member